Contact cleaning circuit



Oct. 22, 1968 R. 0. SLAYTON CONTACT CLEANING CIRCUIT Filed Oct. 7, 1965 INVENTOR RANSOM D. SLAYTON rev/mg l ATTOR Y} United States Patent CONTACT CLEANING CIRCUIT Ransom D. Slayton, Glenview, 111., assignor to Teletype Corporation, Skokie, 11]., a corporation of Delaware Filed Oct. 7, 1965, Ser. No. 493,725 8 Claims. (Cl. 307-137) ABSTRACT OF THE DISCLOSURE An inductor is connected in parallel with the code generating contacts of a telegraph transmitter, and the inductor is energized through the stop segment of a transmitting commutator. When the commutator wiper moves from the stop segment to the start segment, the energizing path for the inductor is opened; and the inductor produces a high voltage pulse across the contacts of sufficient magnitude to burn out contaminants which prevent electrical closure of mechanically closed contacts.

In the electrical machinery that uses contacts to generate and transmit data as in telegraph transmitters, contaminants frequently interfere with contact operation so that even though a contact pair might be physically closed, they could maintain an open circuit because of some minute contaminants keeping the metal elements of the contact pair from going into intimate, electrical contact. This results in erroneous data being generated and in faulty operation of the machinery with which the contacts are used. In the past, telegraph transmitters delivered their signals directly to the telegraph line and thus used transmitting potentials in excess of 100 volts. This was usually suflicient to overcome most common types of contact contamination; but with the advent of electronic data transmission, lower transmitting potentials are used resulting in more severe problems due to contact contamination.

It is an object of the present invention to assure that when a contact pair is physically closed, it is also electrically closed.

, It is a further object of the present invention to prevent contaminants from interfering with the operation of an electrical contact pair operating in a low-voltage circuit.

It is a feature of the present invention to apply across a contact pair a high voltage pulse of insufiicient magnitude to break down the air gap between a mechanicallyopen contact pair but of sufiicient magnitude to bridge a mechanically-closed, but electrically-open contact pair.

, In accordance with the preferred embodiment of the invention as applied to code-generating contacts of a telegraph transmitter, an inductor and series-connected resistor are placed in parallel with the code-generating contacts. A steady current is passed through the inductor and is interrupted after the contact pair is mechanically closed. The voltage pulse generated by the inductor in response to the interruption of its energizing current is applied through the series-connected resistor across the contact pair. If the contact pair is mechanically open, the voltage is insuflicient to jump the contact gap and the voltage subsides with time. If the contact pair is mechanically closed but electrically open, the voltage pulse is of sufficient magnitude to arc across 'the gap and to overcome or burn out whatever contaminant is preventing contact closure. If the contact pair is mechanically and electrically closed, the voltage pulse is dissipated through the series-connected resistor. Once electrical continuity has thus been assured, the inductor is not energized until the contact pair is again opened.

A more thorough understanding of the present invention can be obtained from the following detailed description when considered in conjunction with the accompanying drawing in which the single figure shows a telegraph transmitting circuit having provisions for cleaning the five ice pairs of code-generating contacts of the telegraph transmitter before 'the start of transmission of each telegraph1c character. r

In this type of telegraph transmitter a plurality of pairs of code-generating contacts is selectively closed and opened in a permutative pattern according to the code to be transmitted. A transmitting commutator is provided having one segment individual to each contact pair. This commutator has two additional segments which are used to transmit the synchronizing bits before and after the code bits in the character, as is common in start-stop telegraphy. After a character has been transmitted, the commutator wiper rests on the segment corresponding to the synchronizing bit following the code bits-commonly called the stop pulse. In this stopped or idle condition current is normally conducted through this stop pulse segment to the utilizing device or to a telegraph transmission line until the pairs of code contacts are again set according to the next permutation code and the commutator wiper starts a new cycle of operation.

A telegraph transmitter circuit having code-generating contacts 10 and a transmitting commutator 11 is shown in the drawing. A battery 12 having an on the order of 18 volts provides current and voltage to the telegraph transmitting circuit. The negative terminal of the battery 12 is connected to a common return or ground. The positive terminal is connected to a 300-ohm, current-limiting resistor 13 that limits the current available to the code contacts to 60 milliamperes. During the idle condition of the transmitter, current is conducted from the battery 12, through the current-limiting resistor 13, and through an inductor 14 that connects the current-limitingresistor 13 to a stop segment 16 of the commutator. A commutator wiper 17 electrically connects the stop segment 16 to a collector ring 19 of the commutator during the stop pulse at the end of each character or during idle periods of the telegraph line. The collector ring 19 of the commutator 11 is in turn connected through the electronic transmitter 21 to a common return. The electronic transmitter 21 utilizes the seriati-m electrical current impulses that issue from the commutator 11. In the idle condition of the telegraph transmitter, current flows through the inductor energizing it. This same current flows through the stop segment 16 of the commutator to the collector ring 19 and thence to the electronic transmitter 21.

'The pairs of code-generating contacts 10 can be energized by any one of a number of code inputs. For example, a tape reader, a keyboard, or a fixed-message generator can selectively close the pairs of code-generating contacts according to a permutation code to be transmitted. One of the contacts of each pair of code contacts 10 is connected to a common wire 23 that is in turn connected to the current-limiting resistor 13 so that current is carried from the battery 12, through the current-limiting resistor 13, and to one contact of each of the pairs of code-generating contacts 10. When the contact pairs 10 are permutatively closed, they selectively couple their associated commutator code segments 26 to the currentlimiting resistor 13 so that when the commutator wiper 17 couples a particularv commutator segment with the collector ring 19, current flows from the battery, through the current-limiting resistor; and if the contact pair associated with the particular commutator segment is closed, through the associated commutator segment 26 to the collector ring 19 and thence to the electronic transmitter 21.

This telegraph transmitter circuit can be operated with a keyboard. When a key is depressed, the code generating contacts 10 are selectively closed according to the code of the alphanumeric character represented by the depressed key. Depressing the key also trips a clutch (not shown) which starts the operation of the commutator 11 moving commutator wiper 17 from stop segment 16 to the start segment 24. The start pulse in a start-stop s,407,s1o

telegraph system is normally spacing (no transmitting current) and there is no input-to start segment 24. After commutator wiper 17 passes over start segment 24, it connects the No. 1 code segment 26-1 to theelectronic transmitter. Therefore, commutator wiper 17 couples battery 12 through current-limiting resistor 13 and the No. 1 code generating contact pair 10-1 to the electronic transmitter 21. If the key depressed causes code-generating contact pair 10-1 to be closed, then current is conducted through contact pair 10-1 and commutator segment 26-1 to the electronic transmitter; but if contact pair 10-1 is open, no current is conducted to the electronic transmitter from commutator segment 26-1. The other code-generating contacts 10-2 and the other code segments 26-2 through 26-5 of the commutator 11 are identical to contact pair 10-1 and No. 1 code segment 26-1.

In order to insure that electrical continuity is maintained through a code-generating contact pair that is supposed to be closed by the keyboard, the inductor 14 generates a high-voltage inductive kick when the commutator wiper 17 moves off of stop segment 16 acting as a circuit opener, to break the energizing circuit for the inductor 14. The voltage generated across the inductor 14 by the collapse of its magnetic field is carried to each individual code-generating contact pair 10 by one of the five decoupling resistors 28. In the case of code-generating contact pair 10-1, the voltage generated by inductor 14 is applied to decoupling resistor 28-1, which is of the order of 22,000 ohms, and thence is applied across contact pair 10-1.

If contact pair 10-1 is mechanically open, the voltage generated by inductor 14 is insufiicient to bridge the gap across contact pair 10-1. If no contact pairs 10 are closed, the entire energy of the inductor 14 is dissipated within the resistance of the inductor itself. If contact pair 10-1 is mechanically and electrically closed so that electrical continuity is established across contact pair 10-1, the voltage generated by inductor 14 causes a momentary current pulse to flow through the decoupling resistor 28-1 and contact pair 10-1, dissipating a small portion of energy of inductor 14. If contact pair 10-1 is mechanically closed but electrically open due to a minute particle of material, a chemical residue, an insulating oil film, etc. no current initially flows in resistor 28-1 and the entire voltage generated by inductor 14 is instantaneously applied directly across contact pair 10-1 overcoming or burning out this contamination and establishing continuity through contact pair 10-1. Current then begins to flow through decoupling resistor 28-1 and contact pair 10-1 and the voltage across contact pair 10-1 diminishes to substantially zero as the energy generated by inductor 14 is dissipated. This contact cleaning operation starts immediately when commutator wiper 17 breaks electrical continuity between the stop segment 16 and collector ring 19 of the commutator and is completed while commutator wiper 17 is traversing the first portion of start segment 24.

The decoupling resistors 28 have several thousand times the resistance of inductor 14 (typically 10 ohms or less). Therefore, the current drawn by any one decoupling resistor does not appreciably lower the voltage generated by the inductor 14 and available to the other contact pairs and the dissipation of inductor energy is mostly Within the inductor itself. In addition, the current passing through inductor 14 and the decoupling resistor 28-1 during the period in which wiper 17 is traversing the No. 1 code segment 26-1 or the other code segments 26-2 through 26-5 of the commutator 11, is insignificant compared with the current available to each code commutator segment through current-limiting resistor 13 when its associated code-generating contact pair is closed. Sufiicient discrimination exists in the electronic transmitter 21 to distinguish between these two widely difierent current levels.

In the operation of this transmitter, current initially flows from the battery 12 through current-limiting resistor 13 and inductor 14 to the stop segment 16 and through wiper 17 and collector ring 19 to the electronic transmitter 21. When a code combination is to be transmitted, code generating contact pairs 10 are selectively closed and commutator wiper 17 goes from thestop segment 16 to the start segment 24, deenergizing inductor 14. The collapse of the magnetic field in inductor 14 generates a high voltage which is applied by the decoupling resistors 28 across all of the code contact pairs 10 breaking down any contamination that is impairing electrical continuity between mechanically-closed. contact pairs. The commutator wiper 17 continues moving across the No. 1 code segment 26-1 and then the other code segments 26-2 through 2-6-5 of the commutator 11 until it comes to rest on stop segment 16, reestablishing the energizing path for inductor 14.

Although only one embodiment of the invention is shown in the drawing and described in the foregoing specification, it will be understood that this invention is not limited to the specific embodiment described, but is capable of modification and rearrangement and substitution of parts and elements without departing from the spirit of the invention.

What is claimed is:

1. A circuit for assuring electrical continuity through a contact pair comprising:

a source of current and voltage connected in series with the contact pair;

means connected in series with the contact pair and source for energization by the source when the contact pair is closed;

an inductor having two terminals with one terminal connected to one of the contact pair;

a decoupling resistor connected between the other terminal of the inductor and the other of the contact pair;

a normally-closed circuit opener connected in'series with the inductor and the source completing an electrical circuit from the source through the inductor and the circuit opener and back to the source; and

means for opening the circuit opener after the contact pair has been closed thereby to cause a surge of voltage to be applied across the contact pair.

2. A circuit for assuring electrical continuity through a contact pair comprising:

a source of current and voltage connected in series with the contact pair;

an inductor connected in parallel with the contact palr;

a normally-closed circuit breaker completing a circuit from the source, through the inductor, through the circuit breaker and back to the source; and

means for opening the circuit breaker after the contact pair has been closed whereby a surge of voltage is generated by the inductor'and is applied across the contact pair.

3. A circuit for coupling a source of voltage and current to a utilization device comprising:

a contact pair connected between the voltage source and the utilization device;

an inductor connected in parallel with the contact pair;

a normally-closed circuit breaker connected between one terminal of the inductor and the source; and

means for opening the circuit breaker after the contact pair has been closed whereby a surge of voltage is generated by the inductor and is applied across the contact pair.

4. A system for assuring completion of an electrical circuit from a source of voltage and current to a utilization device through a contact pair comprising:

a contact pair;

an inductor and series-decoupling resistor connected in parallel with the contact pair;

a normally-closed circuit breaker connecting the inductor to the source of voltage and current for energization thereby; and

means for opening the circuit breaker after the contact pair has been closed, whereby the inductor is deenergized and the resulting voltage pulse is conducted through said series-decoupling resistor and is applied across the contact pair to burn out contaminants lodged between the contact pair.

5. A system for assuring electrical continuity through a contact pair comprising:

a contact pair;

an inductor connected in parallel with the contact pair;

means for energizing the inductor with electrical current;

means for rapidly deenergizing the inductor; and

means for applying the voltage generated by the inductor deenergization across the contact pair to burn out contaminants lodged between the contact pair.

6. A telegraph transmitter comprising:

a source of voltage and current having at least two terminals;

a plurality of code-generating contact pairs, one contact of each pair coupled to one of the terminals of the source;

a distributor having a plurality of code segments and two synchronizing segments for sequentially transmitting the output from the code-generating contact pairs, the other contact of every contact pair each connected to an associated code segment;

its associated contact pair, whereby start of the distributor stops conduction of the current through the one of the synchronizing segments of the distributor causing the inductor to generate a surge of voltage that is applied by the resistors across each contact parr.

7. In a circuit containing an electrical contact pair subject to contamination:

a primary source of voltage and current insuflicient to overcome the contamination when the contact pair is closed and means connected in parallel with the contact pair for momentarily applying a voltage across the contact pair of sufiicient magnitude to overcome the contamination each time that the contact pair is closed for the passage of current, said voltage applying means comprising an inductor having a separate energizing path for storing energy between closures of the contact pair, the energy of which is applied across the contact pair in the interval between the time that the contact pair is closed and the time that current is to pass through the closed contact pair.

8. A circuit according to claim 7 wherein the energy of said inductor is applied across the contact pair through an isolating resistor upon the opening of the energizing path of the inductor.

References Cited UNITED STATES PATENTS an inductor having two terminals with one terminal 1,250,152 12/1917 Eisenrnann 307137 X coupled to said one terminal of the source and the 2,758,223 8/1956 Mueller 307-137 other terminal of the inductor connected to the one 2,817,774 12/1957 Knlel et al. 307-137 of the synchronizing segments of the distributor that conducts current durin the idle eriod of the dis- 286O262 11/1958 Sperr 307 137 t t d g P 3,092,739 6/1963 Lode 307137 an 3,229,040 1/1966 Drake et al. 307-137 x a plurality of resistors having two terminals with one terminal connected to the one of the synchronizing segments of the distributor and the other terminal of each resistor connected to the other contact of ROBERT K. SCHAEFER, Primary Examiner.

T. B. JOIKE, Assistant Examiner. 

